In general, environmental regulations require reduction of NOX, CO/HC and the like, which are environmental pollutants. In order to meet these requirements, the exhaust systems of vehicles employ catalysts through a warm-up catalytic converter (WCC) or an under-floor catalytic converter (UCC).
Generally, in order to meet the requirements of environmental regulations, the catalytic performance in the WCC or UCC of reducing NOX, CO/HC is important, and it is very important, as much as the catalytic performance, to prevent NOX and CO/HC from being discharged into the atmosphere due to leak of an exhaust line.
Preventing leaks from exhaust lines is important, particularly, in a turbocharged engine exhaust system in which a turbocharger and a WCC are directly connected to each other. This is because a gasket provided between the connection portions of the turbocharger and the WCC is directly exposed to high-temperature exhaust gasses flowing from the turbocharger to the WCC. Thus the damage risk of the sealing portion of the gasket increases due to a deterioration thereof.
For this reason, attempts to increase the joining force of the gasket to the connection portions of the turbocharger and WCC by employing a plurality of bolts to increase bolting force, and reducing the damage risk of the sealing portion due to high-temperature exhaust gasses by additionally applying a sealing material with strong heat resistance are used.
However, it is inevitable for the gasket to be continuously exposed to high-temperature exhaust gasses which causes deterioration thereof, and such an unfavorable condition accelerates deterioration of the sealing portion adhered to the WCC. Accordingly, the sealing performance between the WCC and the gasket is generally degraded as time passes.
In addition, since vibration due to a shaking of the engine is transferred to the turbocharged engine exhaust system, the turbocharged engine exhaust system is subject to vibrations in which the bolting force fixing the turbocharger, the gasket and the WCC decreases. In such a vibrational state in which the bolting force decreases, degradation of the sealing performance due to deterioration accelerates a loosening of the bolts, such that the sealing performance of the gasket is degraded, thereby increasing a risk of an exhaust gas leak.
Since such degradation of the performance of the gasket in the turbocharged engine exhaust system is inadequate to meet the requirements of environmental regulations such as LEV-III, EU6 and China 5, it is required to develop a gasket for preventing a leak of exhaust gasses in the turbocharged engine exhaust system.